The principal feature of many heart diseases is a reduced supply of energy available to the heart muscle. This can be due to a deficiency of available oxygen or an inefficient conversion of energy derived from heart-muscle respiration to the chemical form (ATP) utilizable in muscle contraction. This process, i.e. respiratory energy coupling, is little understood; however, it has been suggested that this energy coupling may involve changes in structural orientation (conformation) of key respiratory enzymes. This proposed research will investigate the allosteric control of respiration by means of molecular conformation changes in normal heart muscle by the use of Fourier transform infrared interferometry (FTIR spectroscopy). These techniques will be used specifically to detect and measure infrared spectral perturbations of sulfhydryl groups and carbon monoxide complexes associated with Complexes III and IV, two key respiratory enzymes, as a function of respiratory and energy state changes. The ultra-high sensitivity of FTIR spectroscopy permits studies to be made on tissue particulates as well as with isolated cytochromes. We anticipate that these studies will lead to measurements with intact myocardium, and to a better understanding of respiratory needs and control in heart tissue.